public function DatabaseConnection_sqlite::nextId

Retrieves an unique id from a given sequence.

Use this function if for some reason you can't use a serial field. For example, MySQL has no ways of reading of the current value of a sequence and PostgreSQL can not advance the sequence to be larger than a given value. Or sometimes you just need a unique integer.

Parameters

$existing_id: After a database import, it might be that the sequences table is behind, so by passing in the maximum existing id, it can be assured that we never issue the same id.

Return value

An integer number larger than any number returned by earlier calls and also larger than the $existing_id if one was passed in.

Overrides DatabaseConnection::nextId

File

drupal/includes/database/sqlite/database.inc, line 278

Database interface code for SQLite embedded database engine.

Class

DatabaseConnection_sqlite

Specific SQLite implementation of DatabaseConnection.

Code

public function nextId($existing_id = 0) {
  $transaction = $this
    ->startTransaction();

  // We can safely use literal queries here instead of the slower query
  // builder because if a given database breaks here then it can simply
  // override nextId. However, this is unlikely as we deal with short strings
  // and integers and no known databases require special handling for those
  // simple cases. If another transaction wants to write the same row, it will
  // wait until this transaction commits.
  $stmt = $this
    ->query('UPDATE {sequences} SET value = GREATEST(value, :existing_id) + 1', array(
    ':existing_id' => $existing_id,
  ));
  if (!$stmt
    ->rowCount()) {
    $this
      ->query('INSERT INTO {sequences} (value) VALUES (:existing_id + 1)', array(
      ':existing_id' => $existing_id,
    ));
  }

  // The transaction gets committed when the transaction object gets destroyed
  // because it gets out of scope.
  return $this
    ->query('SELECT value FROM {sequences}')
    ->fetchField();
}